Category: Calcium/Bone Disorders

Monitor: 21

21 - A REVERSIBLE CAUSE OF FGF23 INDUCED OSTEOMALACIA

Friday, Apr 26
11:00 AM – 11:30 AM

Objective :

Osteomalacia has been associated with iron infusion therapy. The exact mechanism is not fully understood, but is related to an increase in Fibroblast growth factor 23 (FGF23), a phosphaturic hormone. We present a case of iron infusion induced osteomalcia in a patient with chronic iron deficiency anemia (IDA).


Methods :

A 62-year- old woman with history of osteoporosis, hepatitis C, cirrhosis and IDA being treated with monthly ferric carboxymaltose (FCM) infusion for 18 months presented with recurrent non traumatic pathological fractures. Lab testing showed calcium of 8.9mg/dl [8.7-10.3mg/dl], Albumin 3.7g/dl [3.6-4.8], phosphorus 1.8 mg/dL [2.5-4.5], PTH 63 pg/mL [15-65], alkaline phosphatase 190 u/L [39-117], 25 OH D 30.8 ng/mL [30.0-100.0], fractional excretion of phosphorus 18% [<5%], FGF23 361 RU/mL [44-215], GFR 105 mL/min/1.73. The patient was diagnosed with osteomalacia. She was treated with oral calcium and phosphate. At first, no clear etiology was identified for the increase in FGF23. Ultimately it was determined that her condition was related to FCM therapy. She was switched from FCM to iron sucrose therapy, which resulted in reduction in FGF23 to 82 RU/mL and normalization of phosphorus to 3.3mg/dl.


Results :  


Discussion :

Chronic hypophosphatemia can be FGF23 mediated and is a known etiology of osteomalacia. Case reports have discussed FCM infusion therapy increases FGF23 and the mechanism is believed to be due to inhibition of the cleavage of intact FGF23 into its inactive products. 


Conclusion :

This case highlights the serious impact of undiagnosed renal hypophosphatemia and the need for further studies to identify factors affecting FGF23 levels. We suggest monitoring of phosphate levels while on FCM infusion therapy. 

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Abeera A. Khan

Fellow
Rutgers Robert Wood Johnson Medical School
Eatontwon, New Jersey

I am originally from Pakistan. Did my undergraduate from University of Massachusetts. Went to Medical school At Ross University of Medical school. Finished Residency in Internal Medicine from Jersey Shore University Medical Center in New Jersey. Now I am a second year fellow at Rutgers Robert Wood Johnson.

Ammar Al Akshar

Fellow
Rutgers Robert Wood Johnson Medical School
North Brunswick, New Jersey

Currently doing fellow ship at Rutgers Robert Wood Johnson in Cardiology

Arthur Santora